Field of the Invention
The present invention relates a wind turbine comprising:                a wind turbine tower;        a nacelle provided on the wind turbine tower;        a rotor hub rotatably mounted to the nacelle;        one or more wind turbine blades having a tip end and a blade root, where the wind turbine blade further comprises a pressure side and a suction side connected to each other via a leading edge and a trailing edge, wherein the wind turbine blade comprises a first shell part having an inner surface and an outer surface and a second shell part having an inner surface and an outer surface, where the first shell part comprises a first flange having a first gluing surface, and the second shell part comprises a second gluing surface facing the first gluing surface, and where the two gluing surfaces are configured to be glued together using a glue when the two shell parts are placed on top of each other.        
Description of Related Art
In recent years, the size and power of wind turbines has increased along with the efficiency of the wind turbines. At the same time, the wind turbine blades have increased in size and length and the aerodynamic design has also changed. The wind turbine blade has an airfoil shaped cross-sectional profile where the sizes of the airfoil shaped profiles decrease towards the tip of the wind turbine blade. The wind turbine blade is at the other end configured to be connected to a wind turbine rotor hub where this end typically has a circular cross-sectional profile and a reinforced structure.
Wind turbine blades comprise a sandwich structure having two shell parts glued together along two glue lines typically located in the leading edge and the trailing edge. UK Patent Application GB 2481842 A and corresponding U.S. Patent Application Publication 2013/0170991 disclose such a structure. The structure of the two shell parts is typically reinforced using a number of support elements in the form of shear webs, box beams or other support elements to which the two shell parts may be glued. The shear webs may be placed on spar caps integrated into the shell parts. The support elements may be arranged along the cross-sectional profiles and/or along the length of the wind turbine blade. The two shell parts are typically formed in two separate molds where the support elements are then arranged in one of the molds. The other mold is then placed on top of the other mold after which the shell parts are glued together using an adhesive. The disadvantage of this configuration is that the glue lines form weak points in the structure which may crack or break due to dynamic loads, such as twisting and flapwise/edgewise bending. This could cause the two shell parts to separate and even break off during operation.
The problem with delamination may solved as disclosed in UK Patent Application GB 2481842 A and corresponding U.S. Patent Application Publication 2013/0170991 by arranging a temperature sensor in the glue line before sandwiching the two shell parts together. The sensor may be an optical fiber extending along the entire length of the glue line and is used for controlling the curing process and detecting any de-bonding in the glue lines. The two shell parts form an acute angle relative to each other at the trailing edge, thereby forming a narrow gluing area at the edge to which the glue may be applied. Although the curing process can be improved using the temperature sensor, the structure of the shell parts at the gluing region remains the same. This means that the glue lines still form weak points which are likely to crack or break during operation.
The trailing edge may be configured as a flat back forming a virtual trailing edge where the glue lines are located in the flat back instead of being configured as a sharp trailing edge. Each of the shell parts typically comprises one half of a flat back panel where two halves are glued together using a gluing flange connected to each of the two halves and which extends inwards towards the support elements. This configuration allows the wind turbine blade to have a thicker cross-sectional profile with increased structural strength and higher lift performance as compared to a wind turbine blade with actual trailing edge having the same chord. However, the glue lines still form weak points in the structure which may crack or break to the dynamic loads. This may particularly occur in the transition area where the trailing edge changes from a truncated profile to a thin outwards extending profile, since the gluing surfaces change configuration inside the cross-sectional profiles. In this transition area the inwards extending gluing flange has to be faced out in order ensure a smooth transition to the gluing surfaces on the inner surface of the shell parts.
European Patent Application EP 2341241 A1 and corresponding U.S. Patent Application Publication 2011/0200444 disclose a wind turbine blade having a flat back arranged at the trailing edge. One of the two shells forming the wind turbine blade comprises an L-shaped flange extending outwards from the inner surface of the suction/pressure side and towards the other shell. The free end of the L-shaped flange extends inwards towards the support elements inside the profile where a corresponding inner surface of the other shell is glued to the free end using an adhesive. In another embodiment the lower shell comprises a gluing flange which extends outwards from the inner surface and tilts inwards towards the support elements. The upper shell comprises a flat back panel which extends outwards and away from the inner surface where the inner surface of the flat back panel is glued to the gluing flange of the lower shell. These embodiments both describe a gluing flange which extends inwards along the inner surface; this means that the gluing flange cannot be formed in the same manufacturing step as the shell, since it cannot be pulled out of the mold together with the shell. In order to form the gluing flange, additional manufacturing steps are required for adding the flange to the shell. The gluing process cannot be controlled in a very effective manner, since the inwards extending flange relays on its own strength during the assembly process. This means that there is an increased risk that the gluing flange would bend or flex during the process which in turns means that less pressure can be applied to the gluing surfaces when the two shells are squished together.
International Patent Application Publication WO 2012/019610 A1 and corresponding U.S. Patent Application Publication 2013/0239379 also disclose gluing flanges extending inwards towards the support elements of the blade. The gluing flanges are located on a separate flat back profile that is glued to the trailing edge of the two shell parts in an additional manufacturing step. A positioning device must be used to keep this profile in its position during the assembly process. The positioning device uses clamps or vacuum to hold the flat back profile in place. This adds to the total manufacturing process and increases the complexity and production costs. The inwards extending flanges relay on their own structural strength to ensure a close contact with the shell parts which means that they are likely to flex or bend during assembly and thereby increasing the risk of de-bonding.